/*

 * Copyright (c) 1996, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.io;

/**

 * A character-stream reader that allows characters to be pushed back into the

 * stream.

 *

 * @author      Mark Reinhold

 * @since       1.1

 */

public class PushbackReader extends FilterReader {

    /** Pushback buffer */

    private char[] buf;

    /** Current position in buffer */

    private int pos;

    /**

     * Creates a new pushback reader with a pushback buffer of the given size.

     *

     * @param   in   The reader from which characters will be read

     * @param   size The size of the pushback buffer

     * @throws  IllegalArgumentException if {@code size <= 0}

     */

    public PushbackReader(Reader in, int size) {

        super(in);

        if (size <= 0) {

            throw new IllegalArgumentException("size <= 0");

        }

        this.buf = new char[size];

        this.pos = size;

    }

    /**

     * Creates a new pushback reader with a one-character pushback buffer.

     *

     * @param   in  The reader from which characters will be read

     */

    public PushbackReader(Reader in) {

        this(in, 1);

    }

    /** Checks to make sure that the stream has not been closed. */

    private void ensureOpen() throws IOException {

        if (buf == null)

            throw new IOException("Stream closed");

    }

    /**

     * Reads a single character.

     *

     * @return     The character read, or -1 if the end of the stream has been

     *             reached

     *

     * @throws     IOException  If an I/O error occurs

     */

    public int read() throws IOException {

        synchronized (lock) {

            ensureOpen();

            if (pos < buf.length)

                return buf[pos++];

            else

                return super.read();

        }

    }

    /**

     * Reads characters into a portion of an array.

     *

     * @param      cbuf  Destination buffer

     * @param      off   Offset at which to start writing characters

     * @param      len   Maximum number of characters to read

     *

     * @return     The number of characters read, or -1 if the end of the

     *             stream has been reached

     *

     * @throws     IOException  If an I/O error occurs

     * @throws     IndexOutOfBoundsException {@inheritDoc}

     */

    public int read(char cbuf[], int off, int len) throws IOException {

        synchronized (lock) {

            ensureOpen();

            try {

                if (len <= 0) {

                    if (len < 0) {

                        throw new IndexOutOfBoundsException();

                    } else if ((off < 0) || (off > cbuf.length)) {

                        throw new IndexOutOfBoundsException();

                    }

                    return 0;

                }

                int avail = buf.length - pos;

                if (avail > 0) {

                    if (len < avail)

                        avail = len;

                    System.arraycopy(buf, pos, cbuf, off, avail);

                    pos += avail;

                    off += avail;

                    len -= avail;

                }

                if (len > 0) {

                    len = super.read(cbuf, off, len);

                    if (len == -1) {

                        return (avail == 0) ? -1 : avail;

                    }

                    return avail + len;

                }

                return avail;

            } catch (ArrayIndexOutOfBoundsException e) {

                throw new IndexOutOfBoundsException();

            }

        }

    }

    /**

     * Pushes back a single character by copying it to the front of the

     * pushback buffer. After this method returns, the next character to be read

     * will have the value {@code (char)c}.

     *

     * @param  c  The int value representing a character to be pushed back

     *

     * @throws IOException  If the pushback buffer is full,

     *                      or if some other I/O error occurs

     */

    public void unread(int c) throws IOException {

        synchronized (lock) {

            ensureOpen();

            if (pos == 0)

                throw new IOException("Pushback buffer overflow");

            buf[--pos] = (char) c;

        }

    }

    /**

     * Pushes back a portion of an array of characters by copying it to the

     * front of the pushback buffer.  After this method returns, the next

     * character to be read will have the value {@code cbuf[off]}, the

     * character after that will have the value {@code cbuf[off+1]}, and

     * so forth.

     *

     * @param      cbuf  Character array

     * @param      off   Offset of first character to push back

     * @param      len   Number of characters to push back

     *

     * @throws     IOException  If there is insufficient room in the pushback

     *                          buffer, or if some other I/O error occurs

     */

    public void unread(char cbuf[], int off, int len) throws IOException {

        synchronized (lock) {

            ensureOpen();

            if (len > pos)

                throw new IOException("Pushback buffer overflow");

            pos -= len;

            System.arraycopy(cbuf, off, buf, pos, len);

        }

    }

    /**

     * Pushes back an array of characters by copying it to the front of the

     * pushback buffer.  After this method returns, the next character to be

     * read will have the value {@code cbuf[0]}, the character after that

     * will have the value {@code cbuf[1]}, and so forth.

     *

     * @param      cbuf  Character array to push back

     *

     * @throws     IOException  If there is insufficient room in the pushback

     *                          buffer, or if some other I/O error occurs

     */

    public void unread(char cbuf[]) throws IOException {

        unread(cbuf, 0, cbuf.length);

    }

    /**

     * Tells whether this stream is ready to be read.

     *

     * @throws     IOException  If an I/O error occurs

     */

    public boolean ready() throws IOException {

        synchronized (lock) {

            ensureOpen();

            return (pos < buf.length) || super.ready();

        }

    }

    /**

     * Marks the present position in the stream. The {@code mark}

     * for class {@code PushbackReader} always throws an exception.

     *

     * @throws     IOException  Always, since mark is not supported

     */

    public void mark(int readAheadLimit) throws IOException {

        throw new IOException("mark/reset not supported");

    }

    /**

     * Resets the stream. The {@code reset} method of

     * {@code PushbackReader} always throws an exception.

     *

     * @throws     IOException  Always, since reset is not supported

     */

    public void reset() throws IOException {

        throw new IOException("mark/reset not supported");

    }

    /**

     * Tells whether this stream supports the mark() operation, which it does

     * not.

     */

    public boolean markSupported() {

        return false;

    }

    /**

     * Closes the stream and releases any system resources associated with

     * it. Once the stream has been closed, further read(),

     * unread(), ready(), or skip() invocations will throw an IOException.

     * Closing a previously closed stream has no effect. This method will block

     * while there is another thread blocking on the reader.

     *

     * @throws     IOException  If an I/O error occurs

     */

    public void close() throws IOException {

        synchronized (lock) {

            super.close();

            buf = null;

        }

    }

    /**

     * Skips characters.  This method will block until some characters are

     * available, an I/O error occurs, or the end of the stream is reached.

     *

     * @param     n  The number of characters to skip

     *

     * @return    The number of characters actually skipped

     *

     * @throws    IllegalArgumentException  If {@code n} is negative.

     * @throws    IOException  If an I/O error occurs

     */

    public long skip(long n) throws IOException {

        if (n < 0L)

            throw new IllegalArgumentException("skip value is negative");

        synchronized (lock) {

            ensureOpen();

            int avail = buf.length - pos;

            if (avail > 0) {

                if (n <= avail) {

                    pos += n;

                    return n;

                } else {

                    pos = buf.length;

                    n -= avail;

                }

            }

            return avail + super.skip(n);

        }

    }

}